Oralman, T. 2020. Confronting crunching: A refinement for the care of mice with the desire to crunch. Animal Technology and Welfare 19(1), 89-91.

‘Crunching’ is the term often used to describe the abnormal behaviour of mice that habitually crunch their pelleted diet, causing substrate levels to rise as the crumbs settle on the cage floor ultimately burying the nest. When it ‘comes to the crunch’, the welfare and subsequent cost implications of such adverse behaviour have been difficult to tackle due to the limited options available. However, the innovative use of an inexpensive pulp paper shelf as a ‘cruncher barrier’ not only diminishes the negative effects of crunching but also promotes nesting behaviour without completely inhibiting a mouse’s desire to crunch. The aim of this study was to evaluate the effectiveness of the cruncher barrier and garner the valued opinions of other Animal Technologists. Forty cruncher cages, containing 135 mice were used to assess frequency of food top-ups, base changes and nest scores. Further investigation was conducted on 12 cruncher cages of the same genetic background containing 31 mice, by measuring the daily reduction of food from the hopper for 5 nights without and 5 nights with the cruncher barrier. As a control, 12 non-cruncher cages of the same social housing structure and same genetic background were studied for 5 nights without a cruncher barrier. Nest integrity and complexity gradually declines from day 3 as crunching continues. In support of our hypothesis, the application of a cruncher barrier can be seen to improve average nest scores from day 10 onwards, allowing an extended cage base change period of the cages housing cruncher mice. The cruncher barrier has a significant impact on crunching behaviour: for eight cages, crunching had significantly reduced per mouse; however, four cages had shown a significant increase in crunching per mouse. Unpaired t-test confirmed there is a significant difference between non-crunchers and crunchers pre-cruncher barrier. In conclusion, the cruncher barrier maintains food provisions in the hopper by reducing waste; takes up minimal space in the hopper without hindering ad libitum feeding; improves and increases environmental enrichment for cruncher mice by providing an alternative source of nesting material; enhances longevity of housing conditions, providing a more sustainable lifestyle and a refinement in the care of cruncher mice; and is economical to implement, both in materials and labour.

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